The invention relates to a viewfinder system for a camera, in particular for a movie camera.
In order to view a picture or a picture sequence to be recorded by a still camera, movie camera or videocamera, a viewfinder beam path is diverted from the recording beam path running through the camera objective by means of a beam splitter or a mirror reflex device and is imaged as viewfinder picture by a transmitting optics as a real image, for example on a focusing screen or fiber plate or as an air image, where it can be viewed through an eyepiece and assessed. The viewfinder closure of the camera is formed by an eye closure made from a soft plastic that is applied around the eye to the head of a cameraman and prevents laterally penetrating stray light from degrading the viewfinder image viewed. The eye closure can optionally be designed as an eyepiece cup anatomically adapted to the field of view of the cameraman, or in the manner of a bellows. Usually, a leather cloth is pulled over the anatomically shaped eyepiece cup or over the bellows in order to give a more pleasant contact with the skin.
If the eye of the cameraman is not located at the eye closure, stray light can penetrate into the camera interior via the viewfinder system of the camera in a direction opposite to the viewfinder rays diverted from the recording beam path, be reflected into the recording beam path at the rear side of the camera objective, or be scattered in the viewfinder beam path at the focusing screen or fiber plate, and thereby lead to faulty exposures of film or video pictures, and thus render the film or video recording unusable.
In order to avoid the penetration of stray light into the viewfinder system when a head is not applied at the eye closure, it is known to arrange between the eye closure and the eyepiece a shutter that is connected to a lever guided to the outside of the camera housing, such that the cameraman is able to open the shutter by manual actuation of the lever in order to view pictures with his head applied to the eye closure, and to close it again after viewing pictures but before moving his head from the eye closure. However, this known apparatus for preventing the penetration of stray light into the viewfinder system of a camera presupposes extreme concentration on the part of the cameraman, since premature opening or delayed closing of the shutter when no head is located at the eye closure allows stray light to penetrate into the viewfinder system of the camera and can lead to faulty exposures of the film or video.
For this reason, control apparatuses have been developed for a shutter arranged in the viewfinder system of a camera; with these apparatuses, the pressure of the head against the eye closure opens the shutter via a mechanism, and a spring connected to the mechanism closes the shutter when the cameraman no longer presses against the eye closure with his head. This apparatus for automatically opening and closing the shutter has the disadvantage, however, that pressure is continuously exerted on the field of view about the eye of the cameraman while images are being viewed, and this is felt as being unpleasant.
DE 31 35 950 A1 discloses an apparatus for reducing or masking out the quantity of parasitic light incident in a monocular mirror reflex viewfinder and which includes a light sensitive element that is arranged in the camera viewfinder and outputs a voltage as a function of the parasitic light entering through the eyepiece of the viewfinder. A comparator receives the output signal of the light sensitive element and generates a control signal as soon as the intensity of the parasitic light exceeds a predetermined value. A shutter is closed as a function of the control signal such that parasitic light does not scatter into the optical system of the camera through the viewfinder system and cannot degrade the image quality. Instead of the shutter, an aperture stop or a filter can be used in the known apparatus so that the cameraman can observe the object to be recorded through the viewfinder even when the parasitic light passing into the optical system of the camera is reduced.
So that in the case of the known apparatus for triggering a shutter arranged in the viewfinder beam path the viewfinder rays diverted from the recording beams are not received by the light sensitive element and therefore also lead to a closure of the shutter even when the eye of the cameraman is located at the camera viewfinder, there is provided in the eyepiece arrangement of the viewfinder system a small wall which occludes the viewfinder rays diverted from the recording beam path such that the light sensitive element in the form of a photodiode or of a phototransistor picks up only the parasitic light incident through the eyepiece. Despite this measure, given an appropriately set sensitivity of the device for triggering the shutter it is impossible to prevent the viewfinder rays from the end termination of the viewfinder from being reflected at the eye or the visual aid of the cameraman or at a lens, inserted into the viewfinder, for correcting vision defects, falling onto the light sensitive element and initiating a closure of the shutter even though the eye of the cameraman is located at the eye closure of the camera viewfinder.
A further disadvantage of the known apparatus consists in that given low illumination the shutter is open because of a lack of parasitic light incident in the camera viewfinder, and in the event of suddenly incident parasitic light, for example upon an interchange of light and shade, parasitic light is incident in the viewfinder system for a short time up to the closure of the shutter by a control signal output by the light sensitive element, and leads to faulty exposures.
Furthermore, given a minimum distance of the field of view, surrounding the eye of the cameraman, from the eye closure of the camera viewfinder, parasitic light can penetrate into the viewfinder system of the camera and lead to closure of the shutter given an appropriate setting of the sensitivity of the control device, even though the small quantity of parasitic light would not lead to faulty exposures. In order to enable images to be viewed even in such cases, the known apparatus requires a complicated adjustment of the response threshold of the device for triggering the shutter.